@book { KaufversusMiete,
    title = "Kauf versus Miete",
    author = "Frank {Böckelmann}",
    year = "2001",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832433765",
    url = "https://m.diplom.de/document/219053"
}